As used in sections 139.02 to 139.04, inclusive, of the Revised Code, “federal aid” means all financial assistance of whatever nature offered or extended by the federal government or any instrumentality or corporation created by or pursuant to an act of Congress of the United States, whether such assistance is in the form of a gift, grant, or by purchase of notes or bonds bearing no interest, or bearing interest at a rate not to exceed four per cent per annum.